Somehow I'm going way too fast with not enough powder?

[EXPRESS]

In my .338 win mag, 26" barrel I noticed that after about 250-300 rounds that the load I was using had "sped up". It was a fairly hot 75.5gn of VV N160 pushing a CEB 225 at 2880fps. It went up to around 2960fps. So I dropped back to 71 grains and MV went back to 2880fps. This load had shown some pressure signs with flattened primers, but I hear that it is very common in the Blaser R8 rifles, and this one seems to have a large chamber.

Now I've been testing 300 grain Bergers in the same .338win.
My first tests with VV N560 gave a mv of 2483fps av with 68 grains. Consider that 65 to 72 are the published parameters. With 72 grains I got 2618fps av! That is 338 Lapua territory!
These loads are all about 1mm off the lands, all FL sized cases, charges are weighed on a RCBS beam scale, which is regularly checked and zeroed.
Velocity was measured using a Magnetospeed and Chrono simultaneously, with the chrony giving speeds of a dozen fps more than the Magnetospeed. I have junked the Chrony...

And all this with no discernable pressure signs.

I settled on 68 grains because velocity is acceptable but above all accuracy is phenomenal, shooting into a single ragged hole. Even at 72 grains and 2600fps it's shooting sub MOA, but I just can't get my head around the idea of safely pushing 300 grains at 2600 in a .338 win mag?

Has anyone ever seen this kind of speed from this cartridge in a 26" barrel?

 

[AZShooter]

I just looked at Hodgdon's load data for the 338 Lapua and they used a 24" barrel to get several loads in the 2600-2675 fps range. It would appear that your choice of powder and the extra 2'' of barrel makes it possible to get 2600 fps.

Note Vihtavuori's claim: ''The N500 series of Vihtavuori propellants provide the utmost in performance for added velocity and range with heavy bullets.''

If you can get at least three firings with the brass and the primer pockets don't loosen up I'd say you were good.

Heck I have a 30'' 338 RCM that shoots the 300 gr Berger @ 2525 fps with RL-17 (another high velocity powder) so what you are doing doesn't seem that strange to me.

 

[EXPRESS]

AZ, this is a .338 Winchester mag, not a Lapua, on the Hodgdon site the highest max velocity I could find was 2440fps for the Win mag.

I am getting 2485 with a very mild load, and reaching 2620 with the maximum published load of 72 grains of VVN560. As I've said, there are no other factors I can think of that could influence the pressure/velocity. Air temperature was 26°C while shooting, the ammo and rile had been sat in the shade in a cool spot for several hours before I shot. I like to put my gear out (I shoot from home) and let it settle to ambient temperature in the shade for my records. This afternoon I will be pulling the rifle and ammo out of the freezer (I have a big freezer) and testing it at -20 and 0°C to see what results I get to determine temperature sensitivity.

 

[Grumulkin]

Your big mistake is using velocity as a measure of pressure. It is ridiculous to use a chronograph and then surmise a load is safe or unsafe based on velocity. If your accuracy is acceptable, the bolt lift isn't hard and you don't have other signs of high pressure enjoy the vellocity and don't worry about it.

This myth about velocity being a reliable measure of pressure is wide spread. It is NOT a primary measure of pressure but only a secondary indicator. Just consider that as pressure increases to a dangerous point velocity goes DOWN. Yea, DOWN. At the greatest extreme you have a bolt in your face and the bullet has hardly any velocity at all.

 

[RockyMtnMT]

My only thought that comes to mind is, could there be a possibility of an over sized bore? We received a barrel for a custom project not long ago and the bore was out of spec large. We sent this barrel back. If bore is over size and grove is correct it would make for a fast barrel.

I think using a chrono while working loads is smart. Vel is a sign of pressure, along with all the other indicators. If you ignore the vel while working up to the point of catastrophic failure it may be true that the vel goes down.

Steve

 

[Grumulkin]

The bore could be a little larger than usual but if accuracy/precision is excellent as he says, I woudn't call it over sized.

By the way, I started reloading close to 50 years ago and have NEVER used a chronograph as a criteria of pressure. Once I've worked up a load, I get the chronograph out to get the numbers to calculate trajectories at extended ranges. I also have never damaged a gun.

There was a gunsmith who, as I recall, did velocity on 10 "identical" rifles shooting "identical" loads. There was as much as a 200 fps velocity difference between the rifles.

The rifle in question is a Blaser R 8. As such, there will not be a bolt "lift" as it's a straight pull design. Also, even at higher pressures, there probably won't be sticky extraction so primers and case heads are the things to watch. Primers are normally flattened but if there is still a little curved radius at the periphery of the primers, the pressure isn't excessive.

It's not unheard of for Blaser to have chambers a little out of spec. I call the above cartridge a 300 Weatherby BI (Blaser Improved). You notice at the shoulder there isn't the double radius making the case volume a little bigger. I have no complaints though as the rifle is very accurate.

 

[RockyMtnMT]

Most of my 30 years of reloading has been done without a chronograph as well. It doesn't diminish the useful data gathered from using a chronograph.

Steve

 

[Grumulkin]

I will agree a chronograph gives useful data but it is wrong to use a chronograph as a criteria of pressure.

 

[EXPRESS]

Sure I can agree that velocity isnt THE indicator of pressure/excessive pressure. And no, the R8 probably won't ever show symptoms of excessive pressure throug bolt lift, due to the camming action and therefore a leverage advantage.
However the case heads are ok, no engraving and primers aren't flattened beyond what is a normal mild load.

I just did my first temp testing and found that for this load I get about 2.6 fps of decay per 1C drop in temperature. Now to test from 2C to -20C to check that the loss of speed is linear even at extreme temps and tomorrow Ill lest for heat with daytime temps predicted at 34C (93F) or may even warm the ammo up to 37 to get a broader gap to test over.

 

[baldhunter]

Also,some barrels are faster than others with the same load.To give you an example,I've got four 7mags that shoot the same load very well.66.0grs of Reloader -22 with 160gr Nosler Accubond.This is what I get.

Remington Sendero 7mag 26" barrel - 3000fps
Remington 700 7mag with a 24" Douglas barrel - 3050fps
Ruger No.1 V with a 24" barrel - 2900fps
Ruger No. 1 B with a 26" barrel - 3100fps


So you can see the extreme spread is 200fps.That's not a little,that's a lot.

 

[tbrice23]

Has anyone ever seen this kind of speed from this cartridge in a 26" barrel?

I have a new 300wsm barrel that has gained more than 70 fps with the same load at same temp after 200 rounds...SO FAR.
I'm not sure if the velocity gain has plateaued yet, time will tell.
Definitely not complaining.

 

[hemiford]

This thread is interesting to me. (many are, of course).

So then, different guns manifest their overpressure signs differently ?

This might be a big topic.

 

[AZShooter]

Express,

I know it is a 338 win mag. I was trying to point out that your getting 2600 fps or so was not that unrealistic and even though you said it was duplicating 338 Lapua performance. I think if you do more research you'll find the338 lapua can be loaded faster than 2600 fps. Guys on this site have reported loads over 2700 and more. Just because it appears that you are duplicating 338 Lapua velocities (as reported by Hodgdon) doesn't mean you are loading too hot. Maybe this is a bit clearer maybe not. <grin>

 

[Grumulkin]

So then, different guns manifest their overpressure signs differently ?

Yes, they do.

Guns of relativly weak actions such as some shotguns and revolvers will blow up or be damaged before you'll see any indication of pressure on the brass. With these, it's best to stick closely to data in a manual.

Many bolt actions will manifest sticky bolt lift.

In the Thompson/Center Contender, the action becomes hard to open.

In the Thompson/Center Encore, extraction of fired cases becomes sticky.

Some semiautos will start throwing brass more randomly or to a different place.

In an accurate firearm, I've found that after initially tightening, groups will start opening up; sometimes markedly so.